“Truth is ever to be found in simplicity, not in the multiplicity and confusion of things.”

Sir Isaac Newton’s words never rang more true (or perhaps hollow) than after watching “Predestination,” a sometimes entertaining but mostly silly and head-scratching sci-fi thriller directed by the brothers Michael and Peter Spierig.

Whatever truth the film tries to convey about the mysteries of fate and free will gets lost in a dense, overly complicated plot about a “temporal cop,” played by Ethan Hawke, who must time-travel through four decades to stop an elusive terrorist.

Along the way, he recruits to his mission Jane/John, a bitter woman turned man, who may or not be the criminal the cop is seeking. To say any more would probably give away too much. Assuming of course, you can keep up with an endless stream of OMG moments designed to keep you reaching for Advil for your pounding headache.

Time-travel movies are inherently difficult to make because story and characters risk serving as the means to the end instead of the other way around. The “Back to the Future” trilogy remains the gold standard of the genre because flux capacitors and flying DeLoreans aside, the films center on the relatively simple premise of a kid trying to get home without (great Scott!) destroying the universe.

In truth, “Predestination” more closely resembles the far superior “Looper,” with Joseph Gordon-Levitt and Bruce Willis. But “Looper,” while confusing at times, never lets the act of time travel undermine the movie’s intelligence nor the integrity of the main protagonist.

By contrast, “Predestination” is too clever for its own good, a film that relies on schtick and gimmicks rather than honest storytelling.